1. Field of the Invention
This invention pertains to a swimming pool alarm and more specifically to a swimming pool alarm that utilizes a standing wave pattern set up from a sound wave generator to detect unauthorized or accidental entry of an object into the pool.
2. Description of the Prior Art
Swimming pools can be a hazard when left unattended. Many attempts have been made to develop a swimming pool alarm, which when activated, is capable of sounding an alarm when an unauthorized or accidental entry of an object or individual into the swimming pool occurs. The previous attempts are plagued with problems, which in many instances renders the device ineffective or inoperable.
Some of the systems on the market today use water pressure measurement devices in conjunction with diaphragms to detect the pressure differential in the water due to any movement of the water. These systems are susceptible to generating many false alarms, because they are incapable of differentiating between movement in the water caused by wind or leaves and movement due to entry of an object into the water, such as a person.
Another system presently on the market utilizes a mercury switch to detect movement of the water. However, this system is also susceptible to generating false alarms, because again even the slightest movement will activate the switch.
Other types of devices utilize electronic circuits incorporating two probes spaced apart above the water as a switch, such as those described in Australian Patent No. 8821727 and U.S. Pat. No. 3,732,556. An alarm is activated by the closing of the switch with the momentary splash of water between the probes. Again this system is very susceptible to false alarms.
None of the above described systems are capable of differentiating between the different stimuli that cause water movement. U.S. Pat. No. 5,043,705, discloses a device that distinguishes different types of objects in a body of water. A costly complex sonar device is implemented to monitor the bottom of the pool for any objects that are not moving. This invention is designed to scan only specific layers of the pool, such as the bottom or the top layer of the pool, while ignoring all other parts of the pool. A very complex algorithm is implemented to determine when a body is laying still on the bottom of the pool. Thus, this system requires the person to be unconscious and at the bottom of the pool, at which time it may be too late to revive them.
U.S. Pat. No. 4,747,085 described another device which utilizes a transmitter producing a standing wave in the pool and a receiver with circuitry to detect interference in the standing wave. This system is susceptible to false alarms due to the use of a separate transmitter and receiver. This configuration is inherently subject to an effect where vibrations from the transmitter travel directly to the receiver through the pool alarm device casing and pool sides, causing interference with the signal derived from the reflected waves from the pool. False alarms may also be caused by background noise. A major source of background noise is rain and wind, both of which usually create noise which gradually increases in intensity, often rising to levels sufficient to cause the pool alarm to trigger. Unless a method for adjusting the alarm trigger threshold to account for high levels of background noise is provided, the device will be subject to spurious alarms.
Therefore, it is a feature of the present invention to provide an improved swimming pool alarm that is not susceptible to false alarms.
It is another feature of the present invention to provide a pool alarm that can distinguish between an unauthorized entry of a person in the pool and waves or other inanimate objects falling into the pool, such as leaves.
It is yet another feature of the present invention to provide an improved affordable pool alarm.
It is another feature of the present invention to provide an improved pool alarm that can detect the unauthorized or accidental entry of an individual prior to the individual becoming unconscious.
Other features are apparent to those familiar with swimming pool alarms and alarm systems.